Not all masks are created equal

MEGAN BASHAM, HOST: Coming up next on The World and Everything in It: testing masks.

MYRNA BROWN, HOST: Most states require people to wear masks in public. But they also allow a wide range of personal choice when it comes to what kind of mask you wear.

BASHAM: Masks come in all shapes and sizes. But are all masks the same? And how can we tell which ones work and which ones don’t? WORLD’s Anna Johansen reports now on some new research that might help answer those questions.

ANNA JOHANSEN, REPORTER: It’s a bright summer day in Asheville, North Carolina, just after noon. A lot of people are out shopping, getting lunch, or strolling the tree-lined streets. Everyone I’ve seen so far is wearing a mask.

DEREK BRITAIN HARRISON: It’s two layer polyester like material, washable, with elastics that just go behind the ears. 

MADELINE: I think I choose the paper one just because it’s kind of a hassle to keep washing your cloth one every time you use it.

WILL: Me personally, I like the cloth one because it’s fun and has more character to it.

CAROL: I think as long as it covers your nose and fits around your chin… any mask would do.

But is that actually true? To help answer that question, a group of researchers at Duke University put together a fairly simple test.

It started when a local group wanted to distribute masks to people in the area. Organizers wanted to make sure the masks they sent out were actually effective. Here’s David Grass, a research associate from Duke.

GRASS: And so they approached us and then we basically came up with a simple experiment to compare different masks.

Martin Fischer was one of the lead researchers.

FISCHER: So the setup is very simple. 

The researchers used a black box, a laser beam, and a cell phone. The laser beam highlights respiratory droplets…those invisible particles we exhale when we breathe or speak. Then somebody spoke into the box to create those droplets. 

FISCHER: And when you speak and you emit droplets, and as soon as they go through the light sheet, they scatter light so you see a little flash of light that gets recorded by the video camera.

David Grass describes it this way.

GRASS: It’s a little bit like if you point a laser pointer in a dusty room sometimes you see dust particles falling through the laser pointer and it’s the same principle.

The researchers took video of the experiment. Fischer puts on a mask, then positions his face in the hole in the black box.

AUDIO: Laser coming on. Okay.

The laser flicks on in a flash of green light.

AUDIO: Day five, surgical mask, trial one. Stay healthy people. Stay healthy people.

The researchers tested 14 different kinds of masks. With each mask, the speaker said the same phrase five times. Then, the researchers counted the number of respiratory droplets each mask let escape—either through the mask, or around the edges. David Grass says the results weren’t too surprising. 

GRASS: So the best performance so to say, at least in our study for this one person, was a fitted N95 mask. And then the, you know, it goes on with surgical masks are very good and most multi layer cotton masks are also really good.

There was one that stood out: The neck fleece, a simple loop of fabric worn around the neck and then pulled up over the nose. Martin Fischer made note of the number of particles that escaped during the neck fleece test.

FISCHE: What’s noticeable here is that you see lots of particles and lots of little particles. 

Fischer attributes that to the neck fleece itself, breaking up droplets into smaller particles. It appeared to create more droplets than no mask at all.

FISCHER: So this is actually counterproductive because the little particles that get generated from big particles, they tend to hang around longer in the air, they can get carried away easier in the air. So it’s it’s not the case that any mask is better than nothing. 

David Grass says to take that conclusion with a grain of salt. The test didn’t determine that all neck fleeces are bad all the time.

GRASS: Again, this was a single fleece tested with a single person. So this result itself is not too meaningful or strong enough to now say those are not good.

The study itself was never meant to conclusively declare which masks were best.

GRASS: It’s not supposed to be a serious mask ranking because we didn’t take enough data. We didn’t test enough masks.

The researchers didn’t test enough masks of each type to make that conclusion. And they didn’t test the masks on dozens of different people. Masks fit different people in different ways…so what works for one person might not work for another. Grass says the purpose of the Duke study was a little different.

GRASS: So the primary result of the study is actually the platform itself. So basically, our intent was to show, look, this is an easy way you can set up this experiment and then you can test masks yourself.

You’d have to be careful with the laser, but other than that…

GRASS: A skilled high school student or undergrad could perform this experiment, yes.

Fischer says the goal was to raise awareness.

FISCHER: So we certainly encourage everyone to wear masks. But you want to make sure that when you wear a mask and you go to the trouble of making a mask, you make one and wear one that actually helps.

Reporting for WORLD, I’m Anna Johansen in Asheville, North Carolina.


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